__________ © Centre for Advanced Research on Energy
Redesign of automotive brake pedal based on castability analysis
M.N.Sudin
1,2
, F.R.Ramli
1,2
S.A. Shamsuddin
1,2
, M.M.Tahir
1,2
, M.M.Mustafa
1
and M.A. Affan
1 1
Faculty of Mechanical Engineering, Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia.
2
Centre for Advanced Research on Energy, Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia.
Corresponding e-mail: nizamsudinutem.edu.my
Keywords: Automotive brake pedal; castability; design review ABSTRACT – Change of automotive component
material for any particular purposed i.e. weight reduction, cost reduction may affect the manufacturing
process which will influence the final geometry of product. For this reason, an original automotive brake
pedal that was initially made of steel was substituted with aluminum alloy and aim to be manufactured by
casting process. In this research, the design review and modification on the brake pedal was carried out based
on the casting rules. Initial castability evaluation on the original and modified brake pedal design was carried
out using Ansys FLUENT simulation software. The results of the study show that changes on the design
features of an original brake pedal were necessary as to improve its castability.
1. INTRODUCTION
Brake pedal is an important automotive component to stop or reduce the speed of a motor vehicle. At
present, many cars have brake pedal that is made of steel. A brake pedal may consist of three major
components namely brake pedal, rubber foot and switch pad contact [1]. Each brake pedal component has to
undergo a series of sheet forming processes before assembled together by welding process. Changing the
material of a brake pedal to a lighter material such as aluminum may affect the final geometries and the
manufacturing process. Thus, automotive design engineers have to modify the original design of a brake
pedal as to fulfill the new manufacturing process requirement.
In aluminum alloy brake pedal production, casting has an advantage of producing in single process and
suitable to substitute the original manufacturing processes combination of press forming and welding
process [2]. However, castability of brake pedal should be investigate and analyze early in design in order to
form the component without formation of effects such as cracks, segregations, pores or misruns [3]. According
to Ravi [4] there are three major approaches for castability analysis: process simulation, parametric cost
estimation and features-based castability checks. Geometric features such as undercuts, holes, sharp
corners and hot spots were recognized from a solid model of the casting and analyzed by a number of
dimensionless criteria functions. These criteria were developed through a detailed study of design heuristics
used by practicing engineers and were written as functions of geometric attributes of component and tool
features. This paper intends to improve the original brake
pedal design based on castability. An original brake pedal design was evaluated and the geometries that were
critical modified and redesign to a new brake pedal design. The comparison between these two designs was
carried out to prove that the modified brake pedal design is better in terms of castability.
2. METHODOLOGY
The research was carried out in three stages of process as following:
Stage 1: Brake pedal design review Stage 2: Modification of brake pedal
Stage 3: Castability analysis The original brake pedal design was reviewed
based on the casting rules. This is where the steel design of brake pedal shows a potential problem at the joining
region between pedal pad and brake pedal arm due to sharp corner. The critical area was found at the bottom
of this joint. The other locations that have critical area are the sharp corner and edges in the middle of the
brake pedal arm. At the joint between brake pad and brake pedal
assembly the ribs were added according to castability rules such in Figure 1. The added dimension of ribs was
20.2 mm on both sides which is approximately 80 from the total length of the joint. The ribs were also
added in the front and behind of the joint with the dimension of 7.5 mm. According to the castability rules,
the fillet was required to avoid stress concentration. On the other location of brake pedal arm the fillets were
added with the dimension ranging from 1-3.75 mm depending on the part thickness.
Afterwards, the castability analysis of brake pedal designs was performed by using Ansys FLUENT
simulation software. Pressure distribution and temperature changes were used to differentiate the
castability of these two designs. The modified area of pedal pad was chosen as the point for comparison
between the original and modified brake pedal design.
46 Figure 1 Modification Design
3. RESULTS AND DISCUSSION
The result of the comparison between new modification brake pedal and the old brake pedal design
are summarized in Table 1. Table 1 Brake Pedal Comparison Based on Castability
Castability Characteristics
Old Design New Design
Max Pressure kPa 187
151
Temperature K 827
855
Air Entrapment Yes
No Comparing the old designed brake pedal and the
new designed brake pedal, the maximum pressure value was less than the original brake pedal after the addition
of the ribs at the joining sections. High pressure at the surface of the casting may lead to hot tearing which
caused by the non-uniform cooling rate of the material that lead to quicker solidification. Uneven cooling rate
may also cause a misrun when the temperature of the material drops. This happened when the temperature
decreased and solidified earlier before filled up sufficiently into the cavity. The porosity may occur due
to shrinkage of the solidified aluminum. Hot tear, misrun and porosity may occur at the joining location of
the sharp angles at the corners. The effect of high pressure may lead to the
porosity due to entrapment of air that happened at the pedal pad surface where the concentration stresses are
high. This may happened due to the incorrect shape dimension of the joint from thin to thick area and
formed a separation direction of metal flow that was inadequate. The separation of metal flow may cause
cold shut due to the evolution of the gas that had happened. The gas evolved or expanded when it
accumulated at the region area of porosity. The temperature of molten metal is important as it
represents the fluidity of material. High temperature of molten metal may cause causalities of the material to
flow smoothly before it solidified. Low temperature of the casting may lead to solidification of the material
become quicker. This will influenced the flow distribution that could not reached the location to fill the
mold sufficiently due to quick solidification of the material and may lead to defection such as porosity due
to shrinkage of the material. Shrinkage happened due to the material thermal expansion at the time molten metal
when it began to solidify. Significantly the temperature of the original brake pedal showed that the molten metal
was not reachable enough by the end location of the casting
Unlike the new brake pedal, the temperature of the molten metal was as even as the liquids condition. This
showed that the temperature maintained at the melting point condition. When the temperature was high, the
flow of the molten metal increase in time, and the molten metal was able to fill sufficiently into the mold
cavity before solidification. This potentially happened when the molten metal started to solidify before filling
up the cavity. For the new designed, the potential of the defect was probably less due to the temperature of the
molten metal was maintained and helped the flow of the material to fill up sufficiently in the mold cavity.
4. CONCLUSIONS
Based on the result, the ribs and fillet of the design influenced the castability of brake pedal design. The
pressure and temperature elements affected the castability of the brake pedals where they influenced the
fluidity and the flow of the material. New design of brake pedal proved that the casting defect can be
reduced and it will be easier to cast based on the simulation result obtained.
5. ACKNOWLEDGEMENT
The authors would like to thank Universiti Teknikal Malaysia Melaka UTeM for the financial
support under short term grant with reference number PJP2012FKM 46CS01051.
6. REFERENCES [1] N. A. Hamid, “Component Design and material
properties, The design of light weight of an automotive brake pedal” pp.14-22, 2007.
[2] S. Kalpakjian and S.R.Schmidt, “Fundamental of metal casting process” , Manufacturing,
Engineering and Technology, Vol 6, pp261-316. [3] M. D. Sabatino and L.Arnberg “Castability of
aluminum alloys” Transactions of the Indian Insitute of Metals, Vol 62, Issue 4-5, pp321-325,
1999. [4] B Ravi, “Casting method optimization driven by
simulation”, Mineral and Metal Review, vol 34, pp33-34, 2008.
